This invention relates to a flexible sheath for an endoscope the flexibility of which can be freely adjusted.
An endoscope inserted into a narrow coeliac cavity such as the stomach, small intestine or large intestine comprises a flexible sheath allowing for the smooth insertion of said endoscope. However, the flexible sheath generally has its flexibility predetermined. Therefore, the difficulties have been encountered that, since an endoscope operator cannot adjust the flexibility of the flexible sheath to the physical condition of a coeliac cavity into which the flexible sheath is to be inserted, those parts of the coeliac cavity to which the endoscope is applicable are limited.
A colonoscope, a kind of endoscope, is now described. Referring to FIG. 1, a sigmoid colon 2 and a transverse colon 3 partly constituting a colon 1 are not fixed in position, but are readily moved in all ways through the abdominal cavity, and easily deformable. Therefore, a flexible sheath 4 of a colonoscope, put into the colon 1 from an anus 5 passes through the sigmoid colon 2 while being flexed along the inner wall thereof and finally reaches an outlet of the transverse colon 3. Where, however, it is tried to push the flexible sheath 4 beyond said outlet, the flexible sheath 4 is bent, failing to enter the transverse colon 3. Therefore, the conventional process comprises remotely controlling a bending section 6 formed at a distal end of the flexible sheath 4 by the angle control knob on the operation section of the colonoscope to divert the bending section 6 toward the transverse colon 3, holding the bending section 6 at the outlet of the transverse colon 3, thereafter pulling the colonoscope to make the flexible sheath 4 substantially straight as shown in FIG. 2, and again pushing the flexible sheath 4 into the transverse colon 3.
If, in this case, still remaining pliable, the flexible sheath 4 is easily bent when pushed again, even though previously straightened with effort, thus presenting difficulties in entering the transverse colon 3 and the preceding ascending colon.
To eliminate the above-mentioned drawbacks, it is attempted, as shown in FIG. 3, to insert a sliding tube 7 through which the flexible sheath 4 passes into the sigmoid colon 2 while letting the sliding tube 7 slide along the flexible sheath 4 after pushing the flexible sheath 4 up to the outlet of the transverse colon 3. This process prevents the flexible sheath 4 from being bent in the sigmoid colon 2, thereby enabling the flexible sheath 4 to be pushed into the transverse colon 3.
Even if the sliding tube 7 is applied, however, the flexible sheath 4 is bent in the transverse colon 3 all the same. Where, therefore, the flexible sheath 4 is further pushed into the transverse colon 3, the transverse colon 3 which should normally be kept in a horizontal position is pushed downward as shown in FIG. 3 into a U-shape. As a result, a patient feels a considerable pain. Moreover, the flexible sheath 4 has to be elongated by the length of the sliding tube 7, presenting difficulties in operating the colonoscope. Further, that portion of the colonoscope which is surrounded by the sliding tube 7 unavoidably has a larger diameter. This goes contrary to the requirement for the colonoscope to be made as narrow as possible.
Apart from the above-mentioned attempt, it may be contemplated to originally render the forward end portion of the sheath 4 of the colonoscope flexible and the remaining portion of the sheath 4 more rigid than the forward end portion thereof. In this case, the flexible forward end portion of the sheath 4, if made long, can indeed be easily inserted into the sigmoid colon 2 without giving pain to a patient. However, when the colonoscope is tried to be further inserted, the flexible forward portion is bent thereby to meander the sigmoid colon 2 as shown by broken lines in FIG. 4. Conversely, where the flexible foward end portion of the sheath 4 is made short, the sheath 4 lifts the sigmoid colon 2 as shown by chain lines in FIG. 5, if the sheath 4 is further inserted. Eventually, the patient suffers a considerable pain.
To resolve the above-mentioned difficulties, a colonoscope has been proposed which comprises a flexible sheath whose flexibility can be varied, as need arises. Already known is, for example, that type of colonoscope, whose flexible sheath comprises an extendible and contractible tube assembly which is formed of a pair of helical coils. These coils are made by winding metallic belts. One of them is inserted into the other. The turns of both the coils are directed reversely to each other. The assembly is moved through the flexible sheath, thereby adjusting the flexibility of said flexible sheath.
Where, however, an elongate flexible sheath of a colonoscope is made of the above-mentioned type, the extendible and contractible tube assembly has to be moved axially for a considerable distance in order to vary the physical condition of the flexible sheath from the freely flexible state to the rigid condition. As a result, the operation section of the colonoscope is elongated, presenting difficulties in handling the colonoscope. Moreover, the assembly is not always moved uniformly over its entire length. Especially, the distal end portion of the assembly is moved less than its proximal end portion and its intermediate portion. Thus, the flexible sheath tends to bend unevenly. Where, to avoid such drawbacks, the turns of the extendible and contractible tubes are coiled at a small pitch, then the flexible sheath cannot have a small redius of curvature even when the flexible sheath is in a freely flexible state. Moreover, where a coeliac cavity has intricate distortions like those of a large intestine, the flexible sheath of the above-mentioned known type of colonoscope which comprises an extendible and contractible tube assembly fails to closely follow such intricate bending.
Another proposed colonoscope is the type whose flexible sheath comprises a wave-shaped spring ring assembly and a plurality of pull wires. The spring ring assembly consists of a row of plurality of wave-shaped spring rings. Each ring except for the rearmost ring has its wave troughs pressed against the wave crests of the adjacent ring such that they form junctions. Each of the pull wires has its distal end fixed to the corresponding junction of the foremost pair of rings and passes through the respective junctions of other pairs of the rings. According to said another proposed colonoscope, the flexible sheath indeed has its flexibility adjusted in accordance with the extent to which the respective pull wires are pulled toward the proximal end of the colonoscope. But said proposed colonoscope has the drawbacks that where an external stress is applied to the peripheral wall of the flexible sheath, said flexible sheath is not bent arcuately but possibly meanders; when the colonoscope is repeatedly used, the wires passing through the flexible sheath tend to be broken; and since flexible sheath itself is rendered extendible and contractible, the optical fiber bundles passing through said sheath are likely to be damaged under a tensile force or compression force.
Still another colonoscope is the type which comprises a plurality of wires axially passing therethrough, and wherein one end of each of the wires is fixed to the distal end of the flexible sheath and the other end thereof is fixed in the operation section of the colonoscope. The respective wires pass through the corresponding coil springs, and the flexibility of the flexible sheath is adjusted by pushing the coil springs at the other ends of the wires.
With the above-mentioned type of colonoscope, it is difficult to provide the coil springs, all of which have the same spring characteristics. Where, therefore, the coil springs are pushed to render the flexible sheath rigid, the flexible sheath is irregularly bent. Further, where the flexible sheath is bent, the wires passing through the flexible sheath are not bent in the same degree as the flexible sheath, but tend to be straightened. As a result, the wires partly strike or rub optical fiber bundles passing through the flexible sheath and the inner wall thereof, probably leading to the damage of the fiber bundles and inner wall, and consequently are ready to be broken.
An object of this invention is to provide a compact endoscope flexible sheath, whose flexibility can be adjusted easily and unfailingly as need arises in an elongate intricately twisted coeliac cavity, and which can be inserted into the depth of the coeliac cavity without imparting pains to the patient.
Another object of the invention is to provide an endoscope flexible sheath, wherein a maximum rigidity is predetermined for the respective sections of the flexible sheath, thereby enabling the overall flexibility of said flexible sheath to be varied as need arises in conformity to the internal physical condition of a coeliac cavity.